Potassium fertilization effects on yield and longevity of established alfalfa

Abstract

Limited information is available which describes the response of established alfalfa (Medicago sativa L.) to topdressing applications of K fertilizer in the Southeastern United States. Field experiments were conducted for three years to determine alfalfa response to rates and time of K application. The experiments were established in two‐year old stands of alfalfa on a Decatur silty clay loam (clayey, kaolinitic, thermic Rhodic Paleudults) and a Hartsells fine sandy loam (fine loamy, siliceous, thermic Typic Hapludults) located in northern Alabama. Potassium as KCl was broadcast in the spring prior to regrowth. For split application treatments, the K was applied in early spring and after the second cutting. Annual total K rates ranged from 56 to 596 kg/ha. Potassium fertilization maintained alfalfa stand density on both soils, but the experiment on the Decatur soil was discontinued after two years due to severe stand loss when the lowest rate of added K was used. Alfalfa yields were increased by the application of K and maximum yields occurred when K was applied according to soil test recommendations made by the Auburn University soil testing laboratory. Potassium applications increased the concentration of K, decreased the concentration of Ca and Mg and had little effect on the concentration of N in tissue from the two cuttings sampled. The split application of K did not consistently increase forage production. There was little movement of K below 25 cm in either soil when K rates of 56 to 596 kg/ha/yr were repeated yearly for up to three years.     

Leaf analysis as a guide to sulfur fertilization of legumes

Abstract

Tissue analysis is a diagnostic tool which can be used in identifying S deficiencies and predicting S fertilizer requirements of crops. A water extraction procedure for removal and measurement of inorganic sulfate in plant leaves was developed and assessed as a measure of S availability in four legume crops. Relationships between sulfate concentration and yield were determined for alfalfa (Medicago sativa L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba) and lentil (Lens culinaris) grown on two Saskatchewan soils, with five rates of S fertilizer supply, in a growth.chamber experiment The sulfate concentration in the leaf tissue was measured at the time of seventh leaf and early flowering stages to estimate the current S status of the plants. The results showed significant relationships between the water extractable sulfate in the leaf and the supply of available S in the soils. The water extraction procedure is recommended for routine analyses because of its simplicity and sensitivity.     

Nutrient concentrations of turfgrass and soil test levels as affected by soil media and fertilizer rate and placement

Abstract

There has been a trend toward using sandier growing media on highly trafficked turf areas to combat the detrimental effects of compaction on soil physical properties. Use of sand to modify, or even replace, existing soil also affects the nutrient status of these turf areas and could lead to both macronutrient and micronutrient deficiencies. Greenhouse experiments were conducted to determine the effects of natural organic fertilizer (Milorganite) or micronutrient supplement (Esmigran) applied to the surface or incorporated at several rates on the nutrient concentration of ‘Pennfine’ perennial ryegrass (Lolium perenne L.) grown on quartz sand, a sand‐peat topdressing mix, and a silt loam soil. Effects of Milorganite rate were most apparent on sand and topdressing, and, with at least one soil for one harvest period, increased rates of Milorganite resulted in increased tissue concentration for phosphorus (P), potassium (K), calcium (Ca), sulfur (S), manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn). With Esmigran, increases in tissue concentration due to rate were found for Mn, boron (B), and Zn. Interactions among soil, rate, and application method made it difficult to generalize concerning nutrient availability from these fertilizers. Effects tended to be most obvious with sand and were more apparent with surface applications in some cases and with incorporation in others. Tissue analysis was superior to soil testing for assessing the nutrient status of a turfgrass stand.     

Maturity and quality of alfalfa as affected by phosphorus fertility

Abstract

Environmental stresses adversely affect alfalfa (Medicago sativa L.) forage quality through altered plant development; however, the effects of soil nutrient stress on forage quality are not well known. The objective of this study was to determine what effect low soil phosphorus (P) had on alfalfa forage quality. Three preplant incorporated rates of P (0, 29, or 59 kg/ha) followed by five topdressed (during each production year) rates of P (0, 7, 15, 29, or 59 kg/ha)were applied to alfalfa established in two experiments in fall of 1988 and 1989. At each harvest in 1989 and 1990, mean stage by weight (MSW) was determined and forage samples were taken for neutral detergent fiber (NDF) and in vitro true digestibility (IVTD) analysis. In the 0‐ to 15‐cm soil layer, soil P concentrations averaged 6, 11, and 22 mg/kg of dry soil with 0, 29, and 59 kg P, respectively, incorporated. Soil P was not changed in the 15‐ to 30‐cm soil layer. Alfalfa herbage increased in P concentration with increasing P fertility level at some, but not all, harvests analyzed. Alfalfa maturity at harvest and NDF concentration increased with increasing P fertilizer rate, whereas IVTD decreased. Differences among treatments in NDF and IVTD probably were due to differences in plant maturity.     

Influence of boron on other chemical elements in alfalfa

Abstract

The objectives of this study were to determine the effect of three boron rates applied to the soil on the distribution and relative abundance of 12 chemical elements in various alfalfa plant parts at four successive stages of growth.

Plant samples were separated into lower leaves, lower stems, upper leaves, upper stems, and tips. These plant parts were analyzed for Zn, B, Fe, Mn, Mg, Ca, P, K, Na, Al, Si, and Cu.

Results of this study indicated: i. application of B to the soil resulted in increases in concentration of B in alfalfa tissue proportional to the rate of B applied. For most elements, a decrease in concentration was generally obtained when the rate of soil‐applied boron was increased from 6.3 to 12.6 kg/ha;

ii. a continual increase in the B concentration from early vegetative to bloom stage of growth and then, a decrease in the B concentration from bloom to seed set was observed for the entire alfalfa plant;

iii. the concentration of an element found in leaf tissue was generally greater than the concentration in stem tissue. Furthermore, the concentration of an element found in the lower leaves was generally greater than the concentration found in the upper leaves.

     

Petroleum Coke Circulating Fluidized Bed Combustion Product as a Sulfur Source for Alfalfa

Abstract: Petroleum coke circulating fluidized bed (CFB) combustion product is created when petroleum coke is combusted with limestone in a circulating fluidized bed boiler. The CFB product contains high concentrations of sulfur (S), nickel (Ni), and vanadium (V). Using it as a S source is encouraged, but little information is available related to plant responses and environmental impact. The CFB product was applied at rates of 0, 11, 33, and 110 kg S ha^?1 to two agricultural soils (Canfield silt loam and Wooster silt loam). Dry weight of alfalfa (Medicago sativa L.) and S in plant tissue was increased by the S treatments. Concentrations in alfalfa of V were increased but did not reach environmental concern levels. Concentrations in alfalfa of Ni were not increased. In the soils, only total S and plant available S were increased by these materials. No soil contamination problems were observed when CFB product was used as an S source.     

Pressurized Hot Water and DTPA‐Sorbitol as Viable Alternatives for Soil Boron Extraction. II. Correlation of Soil Extraction to Responses of Boron‐Fertilized Alfalfa

Abstract

Pressurized hot water and DTPA‐Sorbitol are two relatively new, proposed alternative soil boron (B) extraction methods for which no data on yield or plant nutrient uptake have been reported for validation. Both methods initially have shown significant correlation with the hot water extraction method in untreated soils as well as soils incubated with various levels of B. The objective of the research was to extract samples of B‐treated soils by using all three extraction methods and correlate the B values obtained to yield, B tissue concentration, and total B removal of alfalfa (Medicago sativa). Greenhouse and field experiments on alkaline and limed acid soils naturally low in hot water‐extractable B were conducted to test alfalfa response to B fertilizer. In the greenhouse, highly significant relationships exist between plant uptake and extractable B with all three methods at varying levels of applied B, but no alfalfa yield response was observed. All three methods result in accurate predictions of plant B tissue concentrations and total B removal. The field experiment exhibited a significant positive relationship between total alfalfa yield and extractable B using hot water and pressurized hot water extractions. Extractable B using DTPA‐Sorbitol was not related to total alfalfa yield in the field experiment. This work, coupled with the earlier incubation studies, supports the pressurized hot water extraction method as an improvement over hot water in diverse soil types. The lack of relationship in the acid soil supports DTPA‐Sorbitol as an improvement over hot water in alkaline soils.     

Comparison of MnSO4 and MnEDTA for soybeans grown on two soils in the greenhouse

Abstract

A greenhouse experiment was conducted to compare MnSO₄ and MnEDTA as Mn sources. Four soil‐applied rates of each source were applied to two Coastal Plain soils, a Leefield s (pH 6.3) and an Alapaha is (pH 7.0). Plants were grown for 40 days and dry tissue weights were recorded along with leaf contents of Mn, Zn, Fe and Cu. The same ions were extracted from the soil with DTPA. The chelate source caused no differences in either extractable soil Mn or plant Mn between soils or among rates even when added at its highest rate of 2 μgMn/g. The sulfate source increased extractable soil Mn and plant Mn over the various rates but more so for the Alapaha soil than for the Leefield. Plant weights were not different between sources except on the averages for the Leefield soil. However, for the Leefield soil and the sulfate source, plant weights were lower for the check than for intermediate Mn rates due to Mn deficiency and lower for the high Ma rate (50 μg/g) presumably due to toxicity. A correlation coefficient of 0.866** was obtained for soil‐extracted Mn versus plant Mn concentration indicating that the DTPA was a good extractant for these two soils. High correlations between plant and soil Mn versus plant and soil Zn, Fe, and Cu for the chelate source showed that the MnEDTA affected metal ion availabilities other than just Mn. It was concluded that the MnSO₄ was the better source at the rates used and that for these soils the best rate was S μgMn/g applied to the soil.     

Alfalfa responses to foliar and soil applications of manganese

Abstract

Manganese (Mn) deficiency often occurs in crops grown on well‐limed sandy soils of the Atlantic Coastal Plain region of the United States. This study was conducted to compare the responses of established alfalfa (Medicago sativa S.) to various application methods of manganese sulfate (MnSO₄) fertilizer. Experiments conducted in farmers’ fields at three New Jersey locations determined the effects of applied Mn on forage yield, tissue Mn concentration, and leaf chlorophyll meter readings. An untreated control was compared to the following treatments: foliar Mn applied once before each harvest, foliar Mn applied twice before each harvest, and a one‐time broadcast Mn application in April Or May at 22.4 kg Mn/ha to the soil surface. The rate of foliar Mn used in 1990 was 1.12 kg Mn/ha and in 1991 was 0.56 kg Mn/ha at each treatment time. Forage yield increases were greater with foliar than soil‐applied Mn but there were no differences between foliar‐applied Mn treatments. Total seasonal forage yields were increased (P<0.05) at all three locations with foliar‐applied Mn but at only one location with soil‐applied Mn. When averaged across all locations, forage yields were 6.4% higher than the control for the foliar‐applied Mn treatments compared to 2.9% higher for the soil‐applied Mn treatment. A Mn concentration of 21 mg/kg was determined as the critical level in the upper 15 cm of alfalfa tissue at the early bloom growth stage. Foliar Mn applied twice between harvests most effectively increased tissue Mn concentrations. Soil‐applied Mn initially increased tissue Mn concentration, but there was little long‐term benefit from this treatment. Applied Mn was observed to improve leaf color and chlorophyll meter readings of Mn‐deficient alfalfa. Results indicate that foliar Mn applied before each harvest was a more effective treatment for correction of Mn deficiency of alfalfa than a one‐time soil application of Mn.     

Effect of root systems on preferential flow in swelling soil

Abstract

Permeability problems on irrigated soils may be alleviated by root systems that increase water flow by creating macropores. Infiltration rates have been shown to increase where plant roots decay and serve as preferential flow paths. For low‐organic‐matter swelling soil, there is a question whether macropores are able to resist the lateral swelling forces of the soil. The objective of this study was to observe preferential water flow paths in a swelling soil under two cropping systems. A Holtville silty clay (clayey‐over‐loamy, montmorillonitic Typic Torrifluvent) was observed in situ. Two crops, alfalfa (Medicago sativa, L.) and wheat (Triticum turgidum, L.) provided sharply contrasting root systems, with wheat possessing fine, fibrous roots; alfalfa on the other hand, has a taproot system. Macropores were observed after applying soil‐adsorbing methylene blue dye to irrigation water. Shrinkage cracks failed to conduct dye after 10 minutes into a flood irrigation. Earthworm (Lubricus terrestris) channels were also not stable. However, decaying roots of alfalfa produced stable macropores, while wheat produced no such macropores. The influence of alfalfa‐root‐induced macropores was demonstrated by the increase in final infiltration rate during alfalfa cropping which agreed with Meek et al.’s (1989, 1990) findings on sandy loam soils.     

Response of wheat to sulfur fertilization

Abstract

Coker 747³ wheat (Triticum aestivum L.) was grown on Keo silt loam (coarse‐silty, mixed, thermic Dystric Fluventic Entrochrepts) with four S sources applied at various rates for two years. The innate S level of this soil was not adequate for optimum grain yield; therefore, additional S significantly increased grain yield and S concentration and decreased N/S ratios in wheat tissue. Minimum S concentration and N/S ratios in plant tissue for maximum yield ranged from 1.3 to 2.73 g S/kg and 9.5 to 19.2, respectively.     

追肥减施下加气对番茄生长及土壤酶活性的影响

[目的] 为探究化肥减施条件下加气对作物生长特性和根层土壤特征的影响。[方法] 通过开展连续2年野外田间试验,以宁夏银北灌区大田栽培番茄为研究对象,设置4组微纳米加气比例(0,5%,10%,15%)和3个追肥(尿素—重过磷酸钙—硫酸钾)水平(180—400—480,135—300—360,90—200—240 kg/hm²)。[结果] 在相同追肥水平下,植株的干物质和营养元素(氮、磷、钾)积累量随加气比例增加而增加,提高加气比例有利于番茄开花坐果期根系磷素积累和果实膨大期钾素积累;在相同追肥水平下提高加气比例5%~15%对应番茄产量增加14.0%~44.2%;在相同加气比例下相对传统施肥模式适当降低追肥水平(-25%)对应番茄产量增加0.4%~9.1%;提高加气比例和追肥水平有利于在番茄开花坐果期和果实膨大期显著提高土壤相关酶(过氧化氢酶、碱性磷酸酶和脲酶)活性,相同追肥水平下提高加气比例5%~15%对应土壤相关酶活性提高27.5%~122.9%。[结论] 在宁夏银北灌区地埋滴灌条件下,为促进植株生长、稳定番茄产量和提高土壤酶活性,适宜的“尿素—重过磷酸钙—硫酸钾”追施水平为180—400—480 kg/hm²(相对传统追肥定额减施25%),适宜的微纳米加气比例为10%。     

Quick extraction and determination of potassium in fresh leaf sap and its use as a guide to potassium fertilization of canola,chickpea, and dwarf sunflower

Abstract

Two simple methods to extract potassium (K) from fresh plant tissues for use as possible quick K tests: i) freeze/squeeze in which the tissue is frozen, thawed and extracted by placement in a syringe, and ii) press in which the sap is extracted by crushing fresh leaves in a garlic press, were evaluated. The K concentration in the leaf sap extracted using the two methods was determined using a hand‐held ion selective electrode meter. Two separate growth chamber experiments were conducted to evaluate method performance. In the first experiment, the relationships of fresh leaf sap K with total plant K and with K availability in the soil were determined using canola (Brassica campestris var. Profit) and wheat (Triticium aestivum var. Biggar). In the second experiment, canola (Brassica campestris var. Profit), chickpea (Cicer arientinum), and dwarf sunflower (Helianthus) were grown on two soils low in available K with six rates of added K. The fresh leaf K extracted by the two methods and measured using portable ion selective electrode were well correlated with total plant K concentration at harvest, and also closely reflected the differences in K availability in the soil as indicated by soil extraction and rates of added K. Among the two methods, the press method using a hand‐held squeezing device is the simplest one. However, the freeze/ squeeze method may be a more suitable predictor of the K availability in plant tissue that is less succulent.     

Influence of P and K fertilization on Phytophthora root rot or excess soil water injury of alfalfa cultivars

Abstract

Phytophthora root rot (PRR) is an important disease of alfalfa (Medicago sativa L.) in wet soils. Excess soil water (ESW) stress is required for the successful infection and development of PRR. The effects of P at 0, 40, and 80 μg.g^‐1 soil and K at 0, 120, and 240 μg.g^‐1 soil (in factorial combinations) on the severity of PRR or ESW stress was investigated on a PRR‐susceptible (Iroquois) and a resistant (Oneida) alfalfa cultivar in a greenhouse trial. P and K applications significantly increased the dry weight of tops prior to imposition of PRR or ESW stress. However, plants subjected to PRR or ESW stress did not respond significantly to P or K and there was no significant effect of P or K on the severity of PRR or ESW injury. The plants subjected to PRR or ESW stress had lower tissue P concentration than those under stress‐free conditions. Increasing P additions resulted in a significant increase in P concentration of Iroquois plants, while in Oneida the response was non‐significant. The response of K concentration in the plant to increasing K additions was dependant on P levels.     

Chlorine concentrations in alfalfa herbage and soil with KCl topdressing of a low fertility silt loam soil

Abstract

The purpose of this study was to determine the amount of Cl in plants and soil following topdressing of alfalfa with increasing amounts of KCl (0–0–60). The study was conducted with Ranger alfalfa on a low K Piano silt loam soil that had been topdressed twice during three years with a total of zero, 203, 406, 1220, and 2034 kg/ha of Cl as KCl (0, 224, 448, 1334, and 2240 kg/ha of K). Herbage was harvested annually three times at first flower plus an early October cut (4 cuts). The 3‐year average herbage yields were highest with 1220 kg/ha of topdressed Cl. Herbage yields decreased with 2034 kg/ha of Cl, but not significantly below that at 1220 kg/ha. Weakened and yellowed plants were noted in the spring of the second harvest year after 2034 kg/ha of Cl had been applied, and the first‐flower herbage contained 1.90% Cl. It was concluded that the weakened condition of the alfalfa was due to excess Cl.

Movement of Cl through the silt loam soil was rapid. The largest concentrations of Cl in the soil two years after the last KCl application were at the 76 to 91‐cm soil depth, the deepest soil sample tested.     

Evaluation of some soil and plant analysis procedures as predictors of the need for sulfur for corn production

Abstract

The objective of this study was to evaluate the usefulness of measures of mineralized sulfur (S), soil sulfate‐sulfur (SO₄‐S), concentration of S in plant tissue, and the N: S ratio in plant tissue as predictors of the need for S in a fertilizer program for corn (Zea mays L.). Data to evaluate the use of plant analysis for S as a predictor were obtained from ten sites where various rates of N and S were applied to corn. Regression analysis was used to relate the S concentration in the ear leaf tissue as well as the N: S ratio in the same tissue to relative yield when the rate of applied N was held constant at a rate of 168 kg/ha. These measures of S in plant tissue were not significantly related to relative yield at sites where there was no response to fertilizer S as well as sites where added S increased yield.

Data from the same sites were used to assess the ability of soil tests to predict the need for fertilizer S. A measurement of extractable SO₄‐S in the surface soil (0–15 cm) was not reliable for predicting the need for S for corn grown on soils with a silt loam texture.

Static incubation techniques were used to evaluate the amount of S mineralized from soil collected from seven sites. The amount of SO₄‐S measured after four and twelve weeks of incubation was curvilinearly related (p <.05) to yield increase from a S fertilizer. Net mineralized S was less than 2.1 and 3.7 ppm SO₄‐S after four and twelve weeks of incubation, respectively, for soils taken from sites where response to fertilizer S was obtained. Data collected in this study indicate that a measure of mineralized S could improve the ability to predict S needs for corn production on soils with a silt loam texture and a low organic matter content.     

Land application of crushed gypsum wallboard waste for alfalfa

Abstract

Three seasons of research that evaluated the effect of the land application of crushed gypsum wallboard waste (CW) for alfalfa were conducted at four Wisconsin locations having differing soil types and climatic conditions. Material was applied at rates up to 36.0 Mg ha^‐1 preplant and 2.2 Mg ha^‐1 topdress. The highest application of CW pre‐plant showed a positive trend for increased yield of alfalfa at three of the four locations, although this response was not statistically significant. Stand density was not affected with the exception of one year at one location for which the stand was lower where the highest rate Of CW was applied. The soil pH decreased slightly where high rates of CW were applied, presumably caused by an increase in soil solution hydrogen ions which were displaced from exchange sites. Soil calcium (Ca) and sulfur (S) usually increased, and soil test magnesium (Mg) usually decreased where the highest rate of CW was applied. There was no consistent effect of CW application on the soil test levels of other nutrients. Application of CW generally increased the Ca and S, and reduced the Mg concentrations in the harvested forage. Crushed wallboard appears to be as effective as commercial gypsum fertilizer, although this study did not compare equivalent rates of the two materials. No phytotoxic effects from the direct application of CW were noted. The land application of wallboard was found to have no substantial positive or negative agronomic effect on alfalfa production. This practice provides a reasonable alternative to land filling.     

Sewage sludge incinerator ash effects on soil chemical properties and growth of lettuce and corn

Abstract

Incineration reduces sewage sludge volume, but management of the resulting ash is an important environmental concern. A laboratory incubation study and greenhouse pot experiments with lettuce (Lactuca sativa L.) and corn (Zea mays L.) were conducted to examine the potential for recycling elements in sewage sludge incinerator ash in agricultural systems. Ash rates in both the laboratory and greenhouse were 0, 0.95, 3.8, 15.2, and 61.0 g/kg soil (Typic Hapludoll). Ash was also compared to equivalent rates of citrate soluble P from superphosphate fertilizer in a soil‐less growth medium. During soil: ash incubation, Olsen P and DTPA extractable copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) increased with incubation time at the higher ash rates. Release rates diminished rapidly, however, and the limited release of these elements after 280 days was associated with decreasing pH. In the greenhouse, ash amendment increased extractable soil P, plant tissue P, and the growth of lettuce and corn. Ash was a less effective P source than superphosphate fertilizer in the soil‐less growth medium and Olsen P levels were more consistent with these differences than Bray P. Ash increased extractable soil levels and plant tissue concentrations of calcium (Ca), magnesium (Mg), sodium (Na), Cu, and Zn, but extractable soil manganese (Mn) and plant tissue Mn decreased. Ash increased soil pH and extractable SO₄‐S. DTPA extractable Cd and Pb increased, but chromium (Cr) and nickel (Ni) decreased. Lettuce accumulated higher amounts of these trace metals than corn, but tissue concentrations were at control levels or below detection limits in both crops.     

The relationship between phosphorus and copper concentrations in wheat

Abstract

Poorly managed kaolinitic soils are often too low in P and K for optimum agronomic crop production. Even though many of these soils have relatively high phosphate fixing capacities, P applied at sufficient rates to increase soil P to acceptable levels may induce micronutrient deficiencies. The purpose of this study was to evaluate the effects of applied and residual P on Mn, Zn, and Cu uptake by field grown wheat (Triticum aestivum). Treatments were a one‐time application of P (0, 64, 128, 256, and 384 kg/ha P) and K (0, 110, 220, 440, and 660 kg/ha K) rates arranged in a 5×5 complete factorial. The treatments were applied in October, 1977 and the study was continued through June, 1979. Potassium and P × K interactions did not have a significant effect on Mn, Zn, or Cu uptake. Phosphorus did not affect Mn concentration in the wheat tissue but Zn and Cu concentrations generally decreased as applied and residual soil P levels increased. The tissue Zn concentration at the various plant growth stages did not decrease below defined critical levels. The Cu concentration decreased linearly with applied P and curvilinearly with residual P. The tissue Cu levels often decreased below suggested critical levels. Total Cu in the wheat tissue indicated that the decrease in Cu concentration as P levels increased was not a simple dilution effect resulting from increased plant growth as applied and residual soil P increased.     

Characteristics,sources, and in situ phytoremediation of polycyclic aromatic hydrocarbon in rural dumpsites

Purpose

Without precaution to deal with gas emissions and leachate generation, dumpsites have become a severe environmental problem in many developing countries. The objectives of this study were to investigate the pollution status of polycyclic aromatic hydrocarbons (PAHs) in dumpsite soil in rural areas of China and to verify phytoremediation effectiveness with Sedum alfredii Hance and alfalfa (Medicago sativa L.) under complex pollution conditions in PAH-contaminated soil.

Materials and methods

In this study, we collected soil cores from four dumpsites in rural areas of North China (Hebei Province) for analysis, and correspondingly conducted an in situ phytoremediation experiment using Sedum alfredii Hance and alfalfa (Medicago sativa L.) at one of these sites, monitoring the total PAH concentration in soil.

Results and discussion

Results showed generally moderate pollution by PAHs in soil samples from dumpsites with pockets of heavy pollution. PAH concentrations in dumpsite soil ranged from 827 to 1101 ng/g (dry weight). High-molecular-weight PAHs were present in higher proportions at oldest dumpsite in operation. Certain molecular ratios of PAHs can be used to diagnose the source of PAHs in soil, and it indicated that the main sources were combustion of domestic coal and biomass, as well as the automobile exhaust and kitchen exhaust. A 17-month in situ phytoremediation experiment resulted in the effective removal of PAHs in the Sedum alfredii and alfalfa plots, with total PAH concentrations decreasing by 82.4% and 81.3%, respectively. Furthermore, PAH concentrations in plants correlated to plant growth conditions.

Conclusions

This study indicated that the soils of the dumpsites were generally moderately polluted by PAHs, and some parts of the area were heavily polluted. Both Sedum alfredii and alfalfa absorbed PAHs from soil, and PAH concentrations in these two plants correlated to the growth conditions of the plants. Phytoremediation can effectively be used for PAH removal in open dumpsites.